This patent application claims priority to Swedish Patent Application No. 0000084-4 filed Jan. 13, 2000.
The present invention relates to a drive unit for a motor vehicle having an internal combustion engine with an output shaft and a gearbox with an input shaft. A first clutch means or mechanism is arranged between the output shaft of the internal combustion engine and the input shaft of the gearbox. An electric machine is coupled to the gearbox and a second clutch means or mechanism, which together with the first clutch means, are arranged so that drive axles of the vehicle are drivable either solely by the internal combustion engine, solely by the electric machine or by the internal combustion engine and the electric machine at the same time.
It has been appreciated that fuel consumption, and thus emissions associated with vehicles driven by internal combustion engines can be reduced if the internal combustion engine is combined with an electric motor. For a given required power, the power/size of the internal combustion engine can be reduced by the corresponding power contribution from the electric motor at the same time as it can be optimized for a narrower rpm and load interval. This could, in total, theoretically provide an increase in efficiency on the order of 40% in such a so-called hybrid engine compared with a pure internal combustion engine of corresponding performance.
A drive unit of the type described by way of introduction is usually referred to as a parallel hybrid, of which there are two main types. In one, the electric motor is placed between the internal combustion engine and the gearbox and acts on the input shaft of the gearbox. In the second, the electric motor is placed after the gearbox and acts on the output shaft of the gearbox; i.e., in principle directly on the drive wheels. Both types have their advantages and disadvantages. The second alternative is preferable as regards drivability and fuel consumption, since the losses between the electric motor and the drive wheels will be minimal. One disadvantage is, however, that the electric motor cannot be used as a starting motor for the internal combustion engine, when the vehicle is standing still. In this case, a separate starting motor will be required. The first alternative does not require a separate starting motor, but the placement of the electric motor between the internal combustion engine and the gearbox, and the torque transmission through the gearbox, results in greater energy losses than with torque transmission directly to the drive wheels.
In view of the above described deficiencies associated with known solutions for drive units for hybrid motor vehicles, the present invention has been developed to alleviate these drawbacks and provide further benefits to the user. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to drive units for motor vehicles and incorporates several additional beneficial features.
The purpose of the present invention is to achieve a drive unit of the type described by way of introduction, which combines the advantages of the two parallel hybrid types described above without having their disadvantages, and which also has additional advantages.
This is achieved according to the invention by virtue of the fact that the electric machine has a rotor, which is joined to an input shaft, forming a second input shaft concentrically arranged with the first mentioned input shaft. The transmission is arranged between the second input shaft and an output element of the gearbox. The transmission has a third clutch means or mechanism for engaging and/or disengaging the drive from the second input shaft to the output element of the gearbox.
With a first clutch engaged, the internal combustion engine is mechanically coupled to the first mentioned input shaft in the gearbox and drives, via its various gearing combinations, the output element of the gearbox; e.g., the crown wheel of a differential built together with the gearbox. Via the other clutches and the gearbox, the electric machine can be coupled either directly to the output shaft of the internal combustion engine, regardless of whether the internal combustion engine drives the vehicle or not, or directly to the output element of the gearbox. When the second clutch is engaged and the first and third clutches are released, the electric machine can be used as a starting motor to start the internal combustion engine when the vehicle is standing still.
In drive units comprising an automatic gearbox of planetary type or a so-called CVT (Continuously Variable Transmission), the shifting is done without any momentary gap, a property which is obtained at the cost of efficiency in comparison with a common step-geared gearbox and disc clutch, where the shifting occurs with momentary gaps when the clutch is disengaged.
In a preferred embodiment of the present invention, the gearbox is a manual or automatic step-geared gearbox in which the first mentioned input shaft has gears engaging gears on at least one secondary shaft. At least one gear in each pair of inter-engaging gears is rotatably mounted on its shaft and lockable to the shaft by clutch means or mechanism. With the first and the second clutches disengaged and the third clutch engaged, the torque can be transferred from the electric machine to the output element of the gearbox at the same time as no torque is transmitted between the internal combustion engine and the output element via the first mentioned input shaft and the secondary shaft. This means that shifting can be effected in the gearbox at the same time as driving force is obtained from the electric machine. As a result, shifting can be effected without any momentary gap. It is thus possible to obtain shifting of equal quality to that provided by an automatic gearbox of planetary type, but without the loss of efficiency caused by the latter.
The beneficial effects described above apply generally to the exemplary devices, mechanisms and methods disclosed herein for the present invention. The specific structures and steps through which these benefits are delivered will be described in greater detail hereinbelow.